1. Field of The Invention
This invention relates to well apparatuses and to anti-rotation devices for well apparatuses used in well operations, such as plugs, jars, float collars, float shoes, cementing stage tools, liner hangers, and clutch devices for packers; and in one embodiment to non-rotating plugs for well cementing operations.
2. Description of Related Art
Once a wellbore has been drilled, operations within the wellbore are facilitated by placing a string of tubular casing in the wellbore so that operations can be conducted in and through the casing rather than in an un-cased wellbore.
For a variety of reasons, cement is introduced into the annular space between the interior wall of the wellbore and the exterior surface of the casing: to form a protective barrier around the casing; to isolate multiple producing formations through which the wellbore extends; and to displace unwanted fluids or material in the annular space between the wellbore and the casing.
After a cased wellbore has been perforated so that production at a particular depth and from a particular formation is achieved, secondary cementing is often employed to force cement into the perforations to seal off the formation, wellbore, and casing. When it is desired to reduce the depth of a wellbore or to place cement at particular points in a wellbore, a technique called "plug back cementing" is employed.
Usually cement is introduced into the annular space between a wellbore and a string of casing by pumping the cement down through the casing, out through the opening at the end of the casing, and back up into the annular space. To prevent the cement from flowing back up into the casing, float shoes and float collars are used at or near the end of the casing. Float collars usually comprise restrictions or shoulders of cement within a tubular member which can be interposed between two casing joints a few joints above a float shoe at the end of the casing string. Either or both of the collar and shoe usually have a check valve which prevents the back flow of cement from the annular space back up into the casing.
A variety of plugs are typically used in cementing operations. These plugs are moved down into the casing by pumping cement or a fluid into the casing on top of the plugs. These plugs accomplish a variety of functions. They provide a divider or separation barrier between the cement on top of the plug and any fluid beneath the plug or between cement beneath the plug and a fluid on top of the plug. Plugs with wipers wipe off the interior surface of the casing as they pass through it. Plugs of sufficient bulk assist in preventing the back flow of cement beneath the plugs.
In a typical cementing operation a collar or shoe, or both, are placed on a casing string and casing is run into the wellbore to a desired level. A bottom pump down plug is then inserted into the casing and wet cement is pumped on top of the plug. The plug moves down the casing, pushing in front of it any fluid, such as drilling fluid or water, which may be present in the casing. The plug moves down until it encounters the float collar. Increased pumping pressure and the weight of the cement above the plug break a diaphragm disposed across a channel that extends through the plug. This permits the cement to flow through the float collar, the weight of the cement forcing open any check valves in the collar or shoe. The cement then flows out from the bottom of the casing, into the wellbore, and up into the annular space between the wellbore and the casing.
To raise the cement to a desired level in the annular space, a top pump down plug is inserted into the casing. Fluid is pumped onto the top pump down plug moving it into contact with the cement. Further fluid pumping pushes the top pump down plug and the cement down into the casing, forcing cement out of the bottom of the casing and further up in the annular space until a desired level of cement is reached. The top plug can be pumped down to contact the bottom plug. The cement then sets and various operations are carried out in the wellbore.
When the well operations have been completed, the plugs, collar and shoe may be drilled out. All of these items are made from drillable material such as plastic, rubber, wood, or drillable metal. The cement in the float collar is also drillable.
Often a rotating drill bit will contact a plug and cause the plug to rotate and then slip on the surface with which it is contact, e.g. the top of a bottom plug or a layer of cement. This slipping is inefficient and wastes time and energy. A variety of prior art devices have addressed this problem. The attempted solutions typically involve the use of some sort of protrusions, projections or teeth on plug ends to prevent rotation or the use of a plate with teeth on both sides that is placed between a plug and a surface over which a plug could potentially slip.
A variety of problems have been encountered with these prior art efforts. Often the teeth on the various devices contact each other and it is then the teeth alone that are forced to bear whatever load is imposed on the plug or plate. These loads can be enormous, crushing or distorting the teeth so that they do not function properly. Other prior art plugs have teeth which are configured and disposed so that the leading edges of the teeth meet and cross, not permitting further engagement of the lateral portions of the teeth. In other plugs the profile, number, and spacing of the teeth is such that any object or debris between the plugs prevents interengagement of the teeth on two adjacent plugs; i.e., the plugs are prevented from accomplishing the desired non-rotating function. With prior art devices in which the teeth are relatively short, slight separation caused for example by a bouncing drill bit off of two tools, e.g. plugs, with such teeth can cause disengagement, relative spinning movement, or ratcheting between the teeth, i.e., the non-rotation function is not accomplished. Previously used protrusions for piercing or gripping rubber may not have sufficient gripping engagement to prevent rotation.
There has long been a need for an effective and efficient structure for preventing the relative rotation of well plugs and other devices and tools during well operations, including, but not limited to, the drill out of plugs and cement. There has long been a need for a structure that keeps teeth or protrusions from preventing the relative rotation of devices. There has long been a need for a structure that prevents teeth or protrusions from bearing large loads which can injure the teeth or protrusions. There has long been a need for a structure which prevents debris or foreign objects from inhibiting the interengagement of such teeth or protrusions. There has long been need for an easily drillable plug.
In accordance with 37 C.F.R. .sctn.1.56, the following are disclosed:
U.S. Pat. No. 4,190,111 discloses a plate with tooth-like protrusions on each side which can be placed between objects in a well such as a plug and a float shoe or collar to prevent their relative rotation.
U.S. Pat. No. 4,836,279 discloses a plug which has downwardly facing elongated projections (rather than teeth and relatively much longer than teeth) and another plug with a plurality of longitudinal recesses (rather than teeth) corresponding to the elongated projections for preventing the relative rotation of the plugs.
"Halliburton's Non Rotating Cementing Plugs," Halliburton Services Sales Technical Data discloses cementing plugs with locking teeth (rather than elongated projections and corresponding recesses) on both the top and bottom plug and on a float collar for preventing plug rotation during drill out.
U.S. Pat. No. 4,711,300 discloses cementing plugs and collars with locking interfaces for preventing relative rotation.
U.S. Pat. No. 3,550,683 discloses a float shoe with slots for receiving a plug with corresponding protuberances on the plug to prevent plug rotation during drill out.
The following are of general interest and provide general information related to plugs and well cementing operations: U.S. Pat. Nos. 3,842,905; 3,006,415; and 4,706,747; Oil Well Cementing Practices in The United States, American Petroleum Institute, page 112, 1959; Halliburton Services Sales and Service Catalog, Volume 4, 1986-87 Composite Catalog pages 2440-2451; Chapter 10, primary Placement Techniques; Weatherford General Services and Products Catalog 1988-89, 1987, pages 4132-4139.